1. Field of the Invention
This invention relates to a semiconductor device and an electronic device by use of said semiconductor device, more particularly to a semiconductor device with a structure of bipolar transistor structure and an electronic device by use of said semiconductor device.
2. Related Background Art
There have been known in the art devices having thin films through which tunnel current flows as the emitter, such as a bipolar transistor (BPT) with an MIS structure, a heterobipolar transistor (HBT) having a micro-crystal (.mu.C) or an amorphous semiconductor as the emitter, etc.
In this case, in the above-mentioned BPT, by utilizing the difference in tunnel probability between electrons and positive holes, the positive holes from the base are impeded by the above-mentioned thin film, thereby effecting reduction of the base current.
However, in the case of the above-mentioned BPT, since the above-mentioned thin film through which tunnel current flows is used, the series resistance of the emitter becomes higher, whereby the reaction is generated between metal and insulation film, whereby reliability may be sometimes lacking. Particularly, since base current leakage occurs in low current region, it is difficult to effect an increase of the current amplification ratio.
More specifically, the above-mentioned BPT with MIS structure of the prior art, for obtaining characteristics for effecting reduction of the above-mentioned base current, will require a necessary minimum thickness of the above-mentioned thin film, whereby the emitter resistance will be increased. On the contrary, if its thickness is too thin, the inhibition ratio of positive holes will be lowered, whereby no reduction of the base current can be effected to lower the current amplification ratio h.sub.FE.
Further, since a difference occurs in tunnel probability between positive holes and electrons, positive holes sometimes cannot become carriers, and therefore although application to the npn type transistor may be possible, application to the pnp type transistor is difficult.
More specifically, in the case when the difference in transmittance of positive holes and electrons is small, inhibition of positive holes cannot be accomplished. Further, although utilization of such difference in transmittance may be applicable to an npn type transistor, it is not applicable to a pnp transistor which is different in junction type. The tunnel probability between positive holes and electrons is determined by the tunnel film, the thickness is sensitively reflected on the current amplification ratio h.sub.FE, whereby variance will readily occur between individual transistors. Further, series resistance may vary similarly in some cases.
On the other hand, in HBT having a micro-crystal (.mu.C) of the prior art, the emitter-base junction, namely the interface between the emitter by use of .mu.C-Si and the base is unstable, and in the low current region of base current, particularly recombination becomes prevailing, whereby the current amplification ration h.sub.FE will be sometimes markedly lowered.
In the case of HBT having an .mu.C or HBT having an amorphous semiconductor as mentioned above, both are weak to heat treatment, thus sometimes lacking stability. Further, there sometimes are problems such that the reaction between .mu.C or amorphous semiconductor and Si single crystal interface occurs, that the context of hydrogen is high to cause an elimination phenomenon of said hydrogen to make the process unstable, or that deterioration may occur during actuation.
More specifically, in .mu.C-Si of the prior art, addition of heat treatment will result in reduction of current amplification ratio h.sub.FE even at, for example, 450.degree. C. Preparation temperature of .mu.C-Si is generally in the range of 300.degree. to 400.degree. C. Such reduction may be considered to be caused particularly by lowering in band gap and elimination of H (hydrogen) contained in .mu.C-Si, etc. because of increased particle size of .mu.C-Si at the Si interface. In .mu.C-Si of the prior art, a large amount of hydrogen is contained during preparation thereof, and also .mu.C-SiO is stabilized by the presence of hydrogen. The surrounding of .mu.C-Si may be considered to be terminated with hydrogen.
In addition, interface defects may sometimes appear, because base current may be leaked in the low current region, or hetero-junctions are present at the pn junction interface.
The BPT with an MIS structure having the above-mentioned structure of the prior art has a lower current amplification ratio h.sub.FE (=I.sub.C /I.sub.B) on the lower current side until, in an extreme case, it become 1 or less, particularly because the recombination current in the oxide film is predominant in the low current region to increase the base current. In the case of such a structure, the reaction between the metal and the insulation film is liable to occur, whereby reliability may be sometimes lacking. Further, since the insulation film has a considerable thickness, the series resistance has become large. Since the tunnel probability between positive holes and electrons is determined according to the thickness of the oxide film, the thickness is sensitively reflected on the above-mentioned h.sub.FE, whereby characteristic variance of individual BPT occurs. The series resistance will also vary similarly. Thus, difficulties are accompanied with stable preparation of all the oxide films at A order.
On the other hand, in the HBT by use of .mu.C of the prior art, as described above, the emitter-base junction, namely the interface between the emitter and the base use of .mu.C-Si is unstable to heat treatment and susceptible to change, whereby stable preparation can be done with difficulty. This is because it is based on instability of the .mu.C itself or instability at the interface with the single crystalline silicon, and further containment of a large amount of hydrogen in ordinary .mu.C which further promotes instability of the crystal. In addition, one by use of .mu.C is susceptible to characteristic deterioration not only during preparation steps but also during actuation.